It seems that the feminist revolution missed something along the way. Here we are in 2007 and women are still discussing the choice between career or motherhood. While some women have managed to do both successfully, most research suggests that there is a "motherhood penalty" whether it is in career opportunities or in long-term salary earnings. (See article in the Mercury News that shares some statistics on this).
Why do men earn more over their lifetime if they have children, while women earn less? As the Mercur News article discusses, often women are forced to try to make their family decisions based on when it will have the least impact on their careers. This often leads to women waiting until their 40's to have children, when then creates a challenge against biology.
Instead of debating the right timing of parenthood, perhaps a more productive discussion is the one on why the world we live in forces us into this debate. When as a society are we going to step up and say that employers and our government need to provide support to parents, particularly moms, who want to raise a family and have a career? It can happen. All we need is some workplace flexibilty, quality childcare, and support and encouragement in the workplace. If the right supports were in place, women would not have to choose between motherhood and career.